Russian authorities are investigating the mysterious death of a prominent journalist who covered military space technology for the Kommersant daily.

Ivan Safronov, 51, fell from a fifth-floor window on Friday at the Moscow apartment block where he lived.

Prosecutors quoted by Russian media say they are investigating the possibility that he was "driven to suicide".

But friends and relatives of Safronov told Kommersant that they knew of no reason why he would commit suicide.

"I don't want to fuel speculation, but I can say for sure that I knew him well and he showed absolutely no sign of being suicidal," said Kommersant's chief editor Andrei Vasilyev.

Safronov had irked some officials with his critical reporting and had been questioned by the Federal Security Service (FSB), the Associated Press reports.

Kommersant says the results of medical tests on his body are expected on Wednesday and that prosecutors will then decide whether to open a criminal case under the article of suspected murder or induced suicide.

Kommersant says its own analysis of his last telephone calls gives no grounds to suspect that he could have been provoked into committing suicide.

Russian investigators are still trying to find out who killed Anna Politkovskaya, a journalist who exposed serious human rights abuses in Chechnya. She was shot dead in Moscow last October.